Addressable displays have been available for many years. U.S. Pat. No. 3,631,286 created a display by creating a sandwich stack of a first array of electrodes, a continuous layer of phosphor, and a second array of electrodes. When a potential is imposed across the phosphor layer by maintaining a pair of electrodes, one for each array at different potentials, light will be emitted from the phosphor layer therebetween. The electrodes of the second array are provided with openings through which the light emitted by the emitting phosphor layer is viewed. The electrodes of the second array have openings which are configured such that the peripheral edge length per unit cross sectional area of the opening enhances or otherwise takes advantage of the intensified fields which exist at the edge of conductors. Such a configuration provides a brighter glow in the regions of the phosphor layer so excited by the intensified fields. While this technique will provide a display with regions in which the phosphor will emit a high intensity glow, other regions of the phosphor will be dimly lit due to the background field created between the two arrays of electrodes. These residual non-zero fields create low intensity illumination or ghost images. Ghost images can also result from stray fields generated by the current in leads used to excite the electrodes if these fields pass through the phosphor layer.
The ghost images from stray fields from wiring have been addressed in the patents of Mark Topp et al, U.S. Pat. Nos. 4,614,668 and 4,665,342. These patents teach that if an array of discrete regions of phosphor is employed with an array of transparent electrodes, the wiring can be patterned to conform to the phosphor free regions and ghost images from the wiring can be eliminated.
Another approach to isolate the display pattern resulting from the application of a field is to configure the electrodes to the desired pattern. U.S. Pat. No. 4,904,901 teaches using shaped transparent electrodes configured to the shape to be displayed. This technique may produce haloes or ghost images about the edges of the electrodes. Also, stray fields introduced by the wiring may result in ghost images. Finally, the technique of the '901 patent limits the regions which can be illuminated.